In general, running or walking involves a specific pattern or sequence of events insofar as the foot is concerned. In particular, the heel impacts the ground first, the weight then shifts forward onto the ball of the foot and next the forefoot and toe region provide the last contact with the ground as the foot is lifted from the ground. The initial impact in the heel area is of special interest with runners because, in general, it is desirable to absorb as much impact energy as possible, consistent with providing a stable landing and without slowing down the runner. A further consideration in a shoe construction of this type is that of actually enhancing the performance of the wearer by, e.g., providing built-in spring force that facilitates the weight shift mentioned above and also assists in propelling the foot off the ground.
A number of patents relate to shoe constructions which are variously designed to address one or more of the issues discussed above. For example, U.S. Pat. Nos. 5,596,819 and 5,437,110 (Goldston, et al.) disclose an adjustable shoe heel spring and stabilizer device for a running shoe including a spring mechanism disposed in the real sole of the shoe and including a cantilevered spring member and an adjustable fulcrum therefor. U.S. Pat. No. 4,492,046 (Kosova) discloses a running shoe which includes a spring wire located in a longitudinal slot in the shoe sole extending from the back edge thereof into the arch region. U.S. Pat. No. 2,447,603 (Snyder) discloses a U-shaped spring plate disposed between the heel of the shoe and overlying a rear portion of the shoe sole. Other U.S. Pat. Nos. of possible interest include: 2,444,865 (Warrington); 3,822,490 (Murawski); 4,592,153 (Jacinta); 5,343,636 (Sabol); 5,435,079 (Gallegos); 5,502,901 (Brown); 5,511,324 (Smith); 5,517,769 (Zhao); and 5,544,431 (Dixon).